Should a country whose constitution prohibits it from using military force overseas be granted membership of a body that dispatches troops to war zones across the globe?

A question for an undergraduate international relations exam, perhaps, but also a very real political conundrum that Japan is eager to see answered in the affirmative.

As the world's second-biggest economy and No 2 contributor to UN coffers after the US, it seems faintly ridiculous that Japan is not a permanent member of the UN security council alongside the US, Britain, France, Russia and China.

Its quest to join them was strengthened this year when the prime minister, Junichiro Koizumi, sent hundreds of troops on a humanitarian mission to southern Iraq despite widespread opposition at home.

That won him kudos in Washington and London, and took the sting out of accusations - made after the first Gulf War - that Tokyo is interested only in bankrolling conflicts while troops from elsewhere take the risks.

But whether that will be enough to convince all five permanent members of the security council - the P5 - of Japan's suitability is open to question.

It does not help that Mr Koizumi himself is a latter-day convert to the UNSC bid. Until recently, he stated publicly that Japan could not mount a serious bid for membership as long as it retained article 9 of its constitution, in which "the Japanese people forever renounce war as a sovereign right of the nation and the threat or use of force as a means of settling international disputes."

Later this month, however, Mr Koizumi will plug his country's bid for permanent status in a speech to the UN general assembly. "I want to express the view that there could be another permanent member of the UNSC of a different type - and that is Japan," he said this week.

Article 9, like the rest of Japanese constitution, was authored by the Americans after the end of the second world war. Now they want to see it ditched, hinting that Japan's bid could fail if it isn't.

Quite how far Washington expects Japan to go in acquiring the diplomatic - read military - mandate to match that of the current P5 is not clear.

This week the Japanese government's top spokesman, Hiroyuki Hosoda, claimed Tokyo had been given assurances that "the US is supporting Japan's membership of the UNSC without any prior conditions."

Yet only days earlier, the US secretary of state, Colin Powell, had this to say: "If Japan is going to play a full role on the world stage and become a fully active and participating member of the security council - and have the kind of obligations it would pick up as a member of the security council - article 9 would have to be examined in that light."

Observers say Japan's best chance lies in allying its membership mission to the general push for UN reform, with an increase in the number of permanent UNSC members - perhaps by as many as five - as the centerpiece. Germany, Brazil, India and South Africa are among the other candidates.

Unity won't necessarily bring results, however. Expanding UNSC membership would require the support of at least two-thirds of the 191-strong membership of the UN general assembly and every one of the P5.

And the P5, of course, includes China. Beijing has so far held its tongue, but Chinese media have made no secret of their opposition to Japan's bid until it is satisfied that its former enemy has sufficiently atoned for its brutal occupation of parts of China before and during the war.

While maintaining that constitutional revision is not a prerequisite for permanent membership, Mr Koizumi is also at the forefront of efforts to rewrite article 9 to allow Japan to play a greater role in, for example, UN-sponsored military operations.

Supporters of article 9 have been using the build-up to his speech in New York on September 21st to remind him that ditching official pacifism is too high a price to pay for the prestige and power afforded by membership of the world's most exclusive diplomatic club.

Mr Koizumi must also fend off accusations that a permanent seat at the UNSC table would make it easier for Washington to dictate Japanese foreign policy - a reasonable charge given Japan's eager participation in the "coalition of the willing."

Those accusations come not only from the pacifist left. Yohei Kono, a former Liberal Democratic party foreign minister and current speaker in the lower house, said, "It is not appropriate to revise article 9 just because the United States urges us to."

A panel set up by UN secretary general Kofi Annan to look into reform is due to report at the end of the year. Japan may be disappointed by what it has to say, particularly if, as many believe, it will recommend the creation of seven or eight semi-permanent seats - minus the power of veto - to be renewed every five years. Japan would probably accept such an offer, but only grudgingly and with assurances that something more substantial will be on offer down the line.

From January, Japan will be given the opportunity to prove its worth as one of the 10 countries granted revolving, two-year membership of the UNSC.

"Japan must think about what it can do to contribute to peace and global security," Mr Koizumi said.

And there is much it can do to prove to the doubters at home and abroad that permanent membership would amount to more than an automatic vote for the US.

Cash aside, Japan has much else to offer - not least a new perspective as the only non-nuclear P5 country - but also in technology, education and humanitarian expertise.

The push for a bigger say in resolving the world's messiest conflicts would be more palatable to many of Mr Koizumi's compatriots if it were based on Japan's abundant strengths, rather than what it is prepared - eventually - to abandon for the sake of greater prestige on the international stage.